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Old 11-27-2007, 05:34 PM   #1
moheybee OP
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Question about my KTM 640's behavior problem

Go easy on me as I'm new to KTMs and thumpers...and no mechanic, but trying to learn.

My bike has about 5.5k miles on it. I had the valves adjusted about 1k miles ago at around 4.5k miles at Scuderia. Recently I've started noticing some oddities that weren't present before. I'm going to take it in to Scuderia, but wanted to hear if anyone on here had any thoughts.

1) Idle hunting around 1500-1700+ when it was rock steady at 1400 after it's valves were adjusted about 1k ago.
I've read the threads regarding Idle RPMs and Idle Hunting and have a Stenhouse screw on the way and I'll start playing around with it when it comes, but I'm wondering if there's more to it...

2) The throttle subtly lurches usually in the 4-5k rev range and in first gear at any rev. It's subtle, but it's there.

3) There seems to be less power similar to when I *temporarily* took the bike up to a higher elevation about 2.5k miles ago.

4) May be unrelated to above, but a) I've noticed there's a rattling that seems a little too loud when the bike is in neutral with clutch out that goes away when I pull the clutch in and b) I started the bike once in first with clutch in and the bike jumped forward and stalled as if it was in gear. It only happened once and I haven't been able to reproduce it, but it was weird either way.

Thanks!

moheybee screwed with this post 11-27-2007 at 05:45 PM
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Old 11-27-2007, 05:42 PM   #2
ram1000
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1. Probably air jet screw adjustment needed
2. ???
3. Did you rejet the bike? If so your altitude change may make it too rich now.
4. I had a GXSR that would rattle the same way when I put too much oil in it. Clutch out it would rattle, clutch in no rattle.
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Old 11-27-2007, 05:46 PM   #3
moheybee OP
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No, I didn't rejet. The higher altitude was temporary and the bike was running fine after the altitude change. Does that matter?

moheybee screwed with this post 11-27-2007 at 05:53 PM
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Old 11-27-2007, 06:03 PM   #4
jamesdemien
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I'd say:
valves
valves
valves or choke not fully disengaged and
the clutch is supposed to sound like that.
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Old 11-27-2007, 06:38 PM   #5
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You're Idle is probably too low. Mine runs best idling around 1800-2000 RPMs. That and you're valves may be a hair to tight/loose.

Actually its supposed to idle at 2000 so I'd try that first.

When my idle was too low it would surge and die going into 2nd gear.
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Old 11-27-2007, 07:25 PM   #6
moheybee OP
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Idle at 2k?!?! The manual says 1400 and I've heard as high as 1600, but never 1800-2000. I'm willing to give it a try, but that seems really high.
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Old 11-28-2007, 05:53 AM   #7
halfcab
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Need to know what year and model the LC4 is. They came with different carbs, maybe some one change out the carb if you bought it used.

It sounds like an air leak to me...a loose/broken vacuum line with a CV carb.

Idle RPM should be around 1200 to 1400. It only needs to be high enough so the auto compression release is deactivated.

I did not work on it, I'm not there so it's only a guess.
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Old 11-28-2007, 06:31 AM   #8
mikeprod92211
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+1 on the vacuum / air leak.
When the tank is off, check for any loose connections, any clamps that need to be tight. Also make sure the electrical connections around the carb are connected. Check for the pinched vent hose from the gas cap!!!!!
That gave me grief for a while!
As far as the clutch goes, welcome to the KTM LC4 clutch world.
They drag, and can drive you nuts while stopped or engine off, but work just fine while riing.
Agree on the idle speed, 1400 - 1600 is fine, or as long you are not stalling and the decomp is not too loud, and bothersome, she'd be fine!
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Old 11-28-2007, 10:00 AM   #9
moheybee OP
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It's a 2006 and I bought it with about 1800 miles on it. The carb was not changed by the previous owner. Thanks for the thoughts guys. I'll take a look today.
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Old 11-28-2007, 12:58 PM   #10
Luke
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Quote:
Originally Posted by moheybee
3) There seems to be less power similar to when I *temporarily* took the bike up to a higher elevation about 2.5k miles ago.
Have you cleaned the air filter recently? Might want to check it.
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Old 11-28-2007, 01:49 PM   #11
meat popsicle
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heya Mo,

from the South Bay area.

A good starting place for setting up (or checking the setup of) your own LC4 is HERE. Creeper goes through the motions for ya. If that doesn't do it then you can work on troubleshooting, but with a bike that has 5,500 miles and was recently serviced by Scuderia (a damn good shop) I would go back to them and ask.

You are correct, KTM recommended idle setting is 1400 but some of La Familia here have found 1600 to work better, perhaps because of the changes recommended in the link above.

Not a troubleshooting guru, but by "throttle lurch" do you mean when you hold the throttle steady it "surges" all by itself? Never heard that brought up here before.

The bike seems to have less power... all of a sudden? Luke's suggestion is a good one, but you should be doing that regularly anyways eh?

If you had the clutch "disengaged" (by pulling the lever in) and the bike still lurched then it didn't disengage. Maybe you just didn't have the lever in as far as you thought?

Just some random thoughts; hope you get the help you need.
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